It's because of Windows 8's fast startup feature.
Temporary solution would be to go back in Windows and restart the system (instead of shutdown). Permanent solution is to disable fast startup.
Recommended solution:
Use ntfsfix in the terminal , even if you can't access Windows.
ntfsfix is a utility that fixes some common NTFS problems. ntfsfix is NOT a Linux version of chkdsk. It only repairs some fundamental NTFS inconsistencies, resets the NTFS journal file and schedules an NTFS consistency check for the first boot into Windows.
If you have dual booted Linux Ubuntu 12.10+ and Windows 8.1 and if you get this error "The disk contains an unclean file system" the use this:
Ctrl+Alt+T and open your terminal:sudo ntfsfix /dev/sda1sudo ntfsfix /dev/sdb1*change sda1 or sdb1 with your partition.
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Ref: askubuntu.com/questions/439634/unable-to-mount-ntfs-hard-drive-partition-the-disk-contains-an-unclean-file-sys
linux.die.net/man/8/ntfsfix
